TEST: Use `--ignore-installed` as workaround of conda
TEST: Use `--ignore-installed` as workaround of conda

`conda` ships with setuptools but lacks a corresponding
easy-install.pth. Attempting to upgrade setuptools using `pip` fails
because easy-install.pth is missing, despite the presentation of the
conda-originating setuptools as an easy_install egg. It is a known bug
of `conda` that is documented at the following:

https://github.com/pypa/pip/issues/2751
https://github.com/ContinuumIO/anaconda-issues/issues/542

tulip-control/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control